Greetings all,
I am a chemical engineer working for a very large chemical firm in the plastics field. I do not claim to be a end all expert, but you see my work every day and do not know it. There might be a doctorate holding professional here that specializes in nothing but PC manufacturing that could argue the finer details better than
I could.
As stated in the thread the bottles are made out of polycarbonate. Oxygen transmissions are of course dependent on time, temperature, thickness, and polymer structure. The most important thing to know is that you cannot group all polycarbonates into the same group for molecular structure design. There are grades that are very permeable and others are nearly the same as PET.
If you were to rank generically the plastic materials used most commonly for fermentation they would fall in this order.
1. PET
2. HDPE
3. PC
However most bottle water bottle manufacturers use a grade of PC with reduced oxygen permeation which would move it slightly behind PET. Not significantly worse in our standards. We expose our glorious liquids to more oxygen in handling then what migrates through the plastic. at least in the short term. I would not suggest a ten year aging process in a polycarbonate bottle, but that is not what most of us is trying to do here. Old beer is generally not thought as highly as old wine.
The biggest trade off for polycarbonate is its chemical resistance to cleaning agents. Which is is fairly poor at in performance. So simply every time you clean your bottle with a harsh agent you are degrading the properties slightly. So with time the effectiveness of the polymer decreases.
So all that to state, polycarbonate water bottles make for a fine short to medium term fermentation chamber, just watch the cleaning agents used.